Geology Reference
In-Depth Information
Bowen's Reaction Series
Bowen's Reaction Series
1300
Ultramafic Units
eg peridotite
1200
1100
Mafic Units
eg Gabbro
1000
900
Intermediate Units
eg Diorite
800
Felsic Units
eg Granite
700
600
500
Figure 3.1
Bowens reactions series and the relation of mineral associations with
composition and temperature of igneous rocks.
basic compositions we may expect from different mineral assemblages. The
naming of most field specimens requires a working knowledge of the natu-
ral variations in their silicate mineral compositions (Section 3.5). Individual
silicate minerals have chemical compositions that vary within predictable limits
(Table 3.1) and it follows that the mineral and chemical compositions of rocks
are closely related. This relationship is also expressed in the most obvious prop-
erty of a field specimen - its
colour -
which is reflected in the colours of its
constituent minerals.
The following terms may be used to describe the characteristics of individ-
ual minerals and the major minerals present within the mode or norm of an
igneous rock.
1. Terms applied to minerals present in the
mode
of an igneous rock and
to rocks having one or more of these minerals as major components of
the mode:
a.
felsic
=
fe
ldspar
+
si
lica (for example, feldspars, feldspathoids for
example,
le
ucite
+
ne
pheline, quartz),
b.
mafic
ferric (for example, olivine, pyroxenes),
c. Mafic
minerals
may also be termed
ferromagnesian
minerals (
fe
rric
=
ma
gnesium
+
+
magnesium
).
